FIG. 1 shows a conventional phased array patch antenna both in plan view (diagram 100, assuming that the antenna is arranged in a horizontal plane) and in cross-section (diagram 102). The antenna comprises an array of square patches 104 which have sides which are each approximately half a wavelength (λ/2) long. For a single patch, the patch 104 and the ground 106 underneath together form a resonant piece of microstrip line with a length of approximately one-half wavelength of the resonance frequency. Such antennas are usually linearly polarized; however a circularly polarized patch antenna can be fabricated by either feeding using two feeds with 90° phase shift between them or by introducing asymmetry in the patch (e.g. by making a slot in the patch).
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known phased patch array antennas.